Cooling system for mechanical rectifier contacts



1958 HANS-JOACHIM KLEINVOGEL 2,863,112

COOLING SYSTEM FOR MECHANICAL RECTIFIER CONTACTS Filed Dec. 2, 1955 k; zvgzem CIKBLING SYSTEM FOR MECHANECAL RECTHFEER CQNTACTS Hans=loachimKleinvogel, Beriin-Siemensstadt, Germany,

assignor to Siemens-Schuckertwerke A. (3., Berlin, Germany, acorporation of Germany Application December 2, 1955, Serial No. 550,715

6 Claims. ((31. 321-48) My invention relates to a cooling system forcooling contacts of a mechanical rectifier, and more specifically to acooling system in which the members coming into contact with the coolingair have a metallic lining which will absorb chemical impurities in thecooling air which are combinable with the mechanical rectifier contactmaterial.

A mechanical rectifier is a mechanically operated switch which works inconjunction with commutating reactors. The switch or contact is usuallyof the type having a pair of stationary contacts and contact engagementand disengagement is then eliected by a bridging contact. Contacts ofthe type used in mechanical rectifiers are clearly shown in co-pendingapplication Serial No. 307,067 filed August 29, 1952, and assigned tothe assignee of the present invention, now iatent No. 2,798,909.

The commutating reactor which is placed in series with. the contact isof the type shown in U. S. Patent No. 2,693,569 assigned to the assigneeof the instant application, and is used to provide a low current step inwhich the contact may be engaged or disengaged. Details of mechanicalrectifier operation and the operation of the contacts in conjunctionwith the commutating reactors is clearly described in both of the abovementioned cases.

in order to obtain the switching of large currents at a high repetitionrate with accuracy and without damage to the parts involved, the movingconductors of the contact such as the bridging contact are made verysmall. Therefore the current density in the contact material attainsvalues of 15,000 to 20,000 amperes per square inch. This current densityis more than ten times higher than the current density used in otherelectrical conductors such as the A.-C. bus and D.-C. bus which aresynchronously connected by the above mentioned bridging contact. Thishigh current density together with the appreciable resistance of thecontact points between the movable conductors and the fixed conductorsof the switch mechanism cause an appreciable amount of heat within arela tively small volume.

For instance, in a practical contact there is approximately two hundredwatts per cubic inch of material. The fixed conductors which are theA.-C. and D.-C. bus leading to the contact mechanism are of very largecrosssection which can be as much as forty to fifty times thecross-section of the movable or bridging contact and permit an easy heatflow away from the small concentrated heat source by conduction.However, the problem still remains to cool these large volume fixedconductors to a relatively low temperature to thereby assure that theactual contact pieces will not get too hot.

The operation of contact elements under high temperature offers manydisadvantages. The first disadvantage would be that the unequalexpansion due to heat of the metallic bus structure which can be ofcopper, the insulators which can be of porcelain, and the frame whichcan be of steel and fasteners which can be steel bolts, as compared thelength of the operation push rods which are usuall constructed of steeland stcatite, cause aptates :Q;

2,863,112 Patented Dec. 2, 1958 preciable difference in contact timingand therefore interfere with the electrical operation. If, for instance,there is only of an inch expansion difference in the above mentionedelements, the contact timing would be changed by 1% electrical degrees.

A second disadvantage of contacts running under high temperature is thatthe excessive heat will cause deterioration of springs which are used tobias the movable contact to the engaged position.

A third disadvantage is that metallic contacts working at high velocityimpact are subjected to high stresses. Furthermore, since they work at ahigh repetition rate which would be 216,000 operations per hour whenrectifying a sixty-cycle source, the high stresses at this highrepetition rate promotes serious mechanical wear. Practical experiencehas shown that this mechanical wear increases tremendously when thetemperature of the contacts exceed approximately C.

Electrical contacts also present problems which are not connected withheat but are caused by contact operation in a corrosive atmosphere.Contacts are metallic bodies which are separated by a layer of gas orair when they are opened and directly touching when closed. The activesurface of the contacts is therefore alternately submitted to theinfluence of the atmosphere and the action of a strong electric currentflowing across this surface from one body to another.

Since practical contacts are made of pure silver or alloy containingsilver, such as silver-nickel, silver-copper, they are very littleaffected by pure air or pure air containing humidity. However, traces ofsulphur, chlorine or their compounds such as H 8, 50 HCl, HClO, areextremely harmful. Furthermore, corrosive or insulating dust creates asimilar problem to that of the above mentioned chemical corrosion.

As mentioned above, cooling of the contacts is essential but cooling thecontacts of a mechanical rectifier mech anism requires tons of air perday and it is obvious that if this amount of air is permitted to come indirect contact with the active contact surfaces, a minute fraction of apercent of the above mentioned dangerous compounds in the air will beextremely detrimental to the contact life.

The principle of my invention is to line the internal surfaces of an airduct or cooling coil which are responsible for carrying or circulatingthe cooling air with a metallic substance which will absorb the abovenoted chemical compounds which, if left in the air, would be absorbed bythe contact surfaces.

By way of example, the cooling duct or cooling coil in the coolingsystem could be lined with copper if the cooling air has a substantialamount of hydrogen sulphide therein. Hence, the copper lining whichpresents asubstantially large surface to the cooling air would absorbsubstantially all of the hydrogen sulphide before it is impinged uponthe contact surfaces.

Accordingly, a primary object of my invention is to provide acirculating system for cooling mechanical rectifier contacts in whichthe circulated air comes into contact with a relatively large surface ofmaterial which will absorb gases or Vapors which would be absorbed bythe contact material.

Another object of my invention is to provide a cooling system formechanical rectifiers which includes a circulating means, air conductingducts and cooling coils wherein the inner surface of the cooling coil,conducting duct or any other body withinthe cooling system is sprayedwith a metal that will chemically react with impurities in thecirculating air that would be absorbed by the rectifier contacts.

Another object of my invention is to provide a cooling system formechanical rectifiers which works in an atice mosphere contaminated withhydrogen sulphide wherein internal portions of the cooling system aresprayed with copper which will thereby react with the hydro-gen sulphideupon the cooperating contacts of the rectifier.

These and many other objects of my invention will become apparent fromthe following description when taken in connection with the figures inwhich:

Figure 1 is a schematic wiring diagram of a mechanical rectifier towhich my novel invention may be applied.

Figure 2 is a perspective view of a pair of mechanical rectifiercontacts with an operating mechanism therefor, in which my novel coolingsystem is applied thereto.

In Figure 1 the source of alternating current is derived from an A.-C.voltage source which energizes the condoctors and passes through thecircuit break ;s Ill to the step down transformer 12. The current issubsequently passed through commutating reactors 13 to step the currentfor commutating purposes as set forth in U. S. Patent No. 2,693,569assigned to the assignee of the instant application. T he constructionof the commutating reactor is described in co-pending application SerialNo. 301,880 filed July 31, 1952, and assigned to the assignee of theinstant application, now Patent No. 2,759,128.

The current then passes through the disconnect switches 14 to thecontact assemblies 115 and 16 which form the subject matter of theinstant application. The contact assemblies and 116, which aresequentially operated in synchronism with the frequency of the source,are con nected to the alternating source buses 10A, B and C to thedirect current load buses 20 and 21.

For purposes of simplification, I have shown in Figure 2 the mechanicalswitching arrangement which is utilized for phase A of Figure 1, itbeing understood that the switching apparatus for phases B and Careidentical in construction.

A synchronous motor drives the shaft 41 which in turn operates theeccentric member 43 to thereby alternately drive the push rods 46 and 47upwardly through the bell cranks 44-. A detailed explanation of theconstruction of the adjustment and control by means 48 is set forth inco-pending application Serial No. 307,024 filed August 29, 1952.

The upward movement of the push rod 47 will urge the disc shapedbridging contact 31 upward against the bias of the helical spring 49 andthereby disengage it i from engagement with the stationary A.-C. contact23 and the positive D.-C. stationary contact as. During this period oftime the push rod as is in its lowermost position and hence the bridgingcontact associated with the structure 16 is biased into contactengagement by the helical spring associated with the contact assembly36.

On the next half cycle, the position of the push rods 46 and 47 will bereversed by the bell crank 44- so that the push rod 47 will be in itslowermost position and the push rod as will be in its uppermostposition. Hence, at this time the bridging contact 31 associated withthe contact block assembly 15 will be in engagement with its associatedstationary contacts 23 and and the bridging contact associated with thecontact block assembly 16 will be disengaged from its associatedcontacts 25 and 2'7.

Thus, throughout a complete cycle of operation the bridging contactswill also complete a mechanical cycle of operation.

The contact structures 15 and of Figure 2 are then shown as being housedin a substantially air tight housing 59 in which a portion 51 has beencut away to allow visual access to the contact structures. The air tighthousing is shown as being attached to an air cooling system whichincludes the ducts 52- and 53, cooling coil 54 and a circulating means5'5 which could be any desired type of blower or fan.

It is to be understood that if the other two phases were shown in thedrawing, the air tight hood 50 could encompass all six contacts, or ifdesired each pair of contacts of the other two phases could have anindividual air tight housing which would be supplied with an air flowbetween the ducts 52 and 53.

in accordance with the essence of the instant invention, a portion 56 ofthe duct 52 has been cut away and an indication has been made therein ofa lining 57 which has been imparted to the duct 52. A similar lining isshown as being imparted to a broken section 53 of the duct 53. Similarlyanother lining could have been made in the ducts of the cooling coil 54-as shown within the cut-away portion 59 of the coil 54.

It is to be realized that the metallic linings 5'7, 53 and 5) could beof different materials, each one being chemically active with respect toa specific air impurity.

Similarly, it is to be understood that the complete duct need not belined and that the complete cooling coil need not be lined. That is tosay, it might be sufficient to merely line a portion of the duct or coilto thereby provide a chemically active surface which is large withrespect to the active surface of the contact surfaces of contacts l5 and16.

As a specific example, assume that the rectifier of Figure 2 operates inan industrial atmosphere having a high concentration of hydrogensulphide. if extreme purity of the air which is circulated through thecontacts 15 and 16 is desired, then it will be apparent that this endcan be achieved by lining either or all of ducts 52, 53 and cooling coil54 with a copper internal surface.

in this case it is obvious that the copper will combine with thehydrogen sulphide, said copper surface being much greater than theexposed silver surfaces of the contacts 15 and 16. Therefore very littlereaction would be found between the hydrogen sulphide which is now at agreatly reduced level and the silver or silver alloy surface of thecontacts 15 and 16.

Although i have shown a preferred embodiment of my invention, it willnow be obvious that many variations and modifications will occur tothose skilled in the art, and i prefer to be bound not by the specificdisclosure herein but only by the appended claims.

I claim:

1. A cooling system for mechanical rectifiers; said mechanical rectifiercomprising a pair of cooperable contacts movable into and out ofengagement with one another and means to synchronously move saidcooperable contacts into and out of engagement with one another, anexposed contact surface of at least one of said cooperable contactsbeing at least partially constructed of silver, said cooling systembeing constructed to direct an air flow on said cooperable contacts forcooling thereof; said cooling system including a means for circulatingair and air passages for conducting air from said circulating means tosaid cooperable contacts; at least a portion of the inner surface ofsaid air passages being copper whereby substantially all impurities insaid cooling air which are combinable with both copper and silver willcombine with said copper surface, said silver surface of said cooperablecontacts being substantially uncontaminated by said impurities.

2. A cooling system for mechanical rectifiers; said mechanical rectifiercomprising a pair of cooperable contacts movable into and out ofengagement with one another and means to synchronously move saidcooperable contacts into and out of engagement with one another; saidcooperable contacts having silver contact surfaces, said cooling systembeing constructed to direct an air flow on said cooperable contacts forcooling thereof; said cooling system including a means for circulatingair and air passages for conducting air fro-m said circulating means tosaid cooperable contacts; at least a portion of the inner surface ofsaid air passages having a metallic lining whereby substantially allimpurities in said cooling air which are combinable with both the metalof said lining and silver will combine with said lining,

said silver surface of said cooperable contacts being substantiallyuncontaminated by said impurities.

3. A cooling system for mechanical rectifiers; said mechanical rectifiercomprising a pair of cooperable contacts movable into and out ofengagement with one another and means to synchronously move saidcooperable contacts into and out of engagement with one another, saidcooperable contacts having silver contact surfaces; said contacts beinghoused in a substantially air tight housing, said cooling system beingconstructed to recirculate an air flow on said cooperable contacts forcooling thereof; said cooling system including a means for circulatingair, air passages for conducting air from said circulating means to saidcooperable contacts and a heat exchanging means; the inner surface ofsaid heat exchanging means having a metallic lining wherebysubstantially all impurities in said cooling air which are combinablewith both copper and silver will combine with said metallic lining, saidsilver surface of said cooperable contacts being substantiallyuncontaminated by said impurities.

4. A cooling system for mechanical rectifiers; said mechanical rectifiercomprising a pair of cooperable contacts movable into and out ofengagement with one another and means to synchronously move saidcooperable contacts into and out of engagement with one another, saidcontacts being composed of a material including silver; said coolingsystem being constructed to direct an air fiow on said cooperablecontacts for cooling thereof; said cooling system including air passagesfor conducting air to said cooperable contacts; said air passages beinglined with a first and second metal, the area of said first and secondmetal linings being large in comparison with the area of exposed contactsurface of said cooperable contacts, said first metal being combinablewith a first impurity in said cooling air, said second metal beingcombinable with a second impurity in said cooling air, said contactsurfaces thereby being substantially unaffected by said first and secondimpurities.

5. In a rectifier for energizing a D.-C. load from an A.-C. source; saidrectifier including a commutating reactor, a pair of cooperable contactsand means for synchronously operating said pair of cooperable contactsinto and out of engagement; said A.-C. source,

commutating reactor, pair of cooperable contacts and D.-C. load beingconnected in series, said commutating reactor providing low currentsteps during operation of said cooperable contacts into and out ofengagement, said cooperable contacts being enclosed in a substantiallyair tight housing, a cooling system for said contacts, said coolingsystem including an air circulating means and passages for conductingair from said circulating means to the contacting surfaces of saidcontacts, said passages having a first and second portion coated with afirst and second metal, said first metal reacting with a first substancewhich also reacts with the material of the cooperable contact surfaces,said second metal reacting with a second substance which reacts with thematerial of the cooperable contact surfaces, said cooperable contactsbeing constructed of a material including silver.

6. A cooling system for electrical contacts; said cooling systemincluding an air circulating means and passages for conducting air fromsaid circulating means to the contacting surfaces of said contacts; atleast a portion of said passages being coated with a metallic substance;said metallic substance being combinable with impurities in the coolingair which are combinable with the material of said cooperable contactcontacting surfaces.

References Cited in the file of this patent UNITED STATES PATENTS1,866,611 Affel July 12, 1932 2,340,098 Zuhlke Jan. 25, 1944 2,525,457Paluev Oct. 10, 1950 2,557,740 Goldstein June 19, 1951 2,584,535 BelaminFeb. 5, 1952 2,741,735 Wasserrab Apr. 10, 1956 FOREIGN PATENTS 22,535Great Britain July 25, 1912 639,336 Germany Dec. 3, 1936 OTHERREFERENCES A Comprehensive Treatise on Inorganic and TheoreticalChemistry (Mellor), Longmans, Green and C0., 1930, vol. 10, page 140.

